Polyvinyl fluoride (PVF) has been manufactured for many years and has found many uses as a protective film or coating over a variety of substrates providing durable and cleanable surfaces. These surfaces are often thin films with the desirable property of being transparent thereby revealing the substrates beneath the film. Alternately these films may be pigmented to provide brightly colored coverings. Current market offerings are hazy and the presence of haze in the films detracts from the aesthetic quality of these coverings and limits their utility.
The fluorine atoms in PVF are largely responsible for its properties of excellent weatherability, chemical resistance and mechanical properties. Enhancement of these properties may be achieved with polymers of higher fluorine content. One way to increase polymer fluorine content is to prepare copolymers in which tetrafluoroethylene (TFE) replaces some of the vinyl fluoride (VF). Such dipolymers have been described by Coffinan and Ford, U.S. Pat. No. 2,419,009 (1947); Sianesi and Caporiccio, J. Polymer Sci., Part A-1, 6, (1968) 335, and U.S. Pat. No. 3,513,116 (1970). The above references describe processes for producing VF/TFE dipolymers. Coffinan and Ford describe an aqueous polymerization process using benzoyl peroxide initiator in the presence of vinyl fluoride monomer, such a process requiring elevated pressures. Sianesi and Capriccio describe preparation of the dipolymers in nonaqueous media such as alcohols or alcohol/water mixtures by using organometallic compounds as initiators, which process can be carried out at substantially reduced pressures. Polymers produced from these prior art methods have nonionic end groups on the polymer chains formed. These nonionic end groups are typically alkyl or aryl and, therefore, hydrophobic in nature.
Stilmar, U.S. Pat. No. 3,531,441 (1970), reported preparation in nonaqueous media of tri- and tetra-polymers composed of VF, TFE and a neutral polymerizable vinylidene monomer free of aromatic groups and free of halogen groups attached to the vinylidene group. The interpolymers of Stilmar were also formed with nonionic end groups.
Heretofore, the prior art teachings have not addressed the need for a polymer with high fluorine content which produces films with the properties desirable for protective coverings and with minimal haze. Furthermore, there are no known solvents for PVF and VF/TFE resins at ambient temperatures. Protective surfaces using these resins were previously prepared by laminating a preformed film, requiring special equipment and expertise, or by coating using a dispersion containing a latent solvent that must be processed at excessively high temperatures. Such methods are not practical for field application of these coatings or for repair of their surfaces damaged in use.